This research project is concerned with describing the ontogeny of homeostatic regulaton (i.e., feeding and drinking) of rats, with special emphasis upon the neural control of homeostatic regulation. Basically, the research utilizes three orientations; behavioral analysis, determing the effects of brain damage sustained during infancy, and evaluating single neuron response characteristics. The first series of experiments are determining when, during ontogeny, infant rats show consumatory behaviors in response to adequate stimuli for thirst (i.e., cellular dehydration, decreased vascular volume, or a combination of the two). The second series of experiments are assessing the effects of destruction of central nervous system areas (e.g., lateral hypothalamic area, lateral preoptic area), when damage is sustained pre- and post-weaning, upon the development of homeostatic regulation. Of specific concern here are determining which regulatory abilities are temporarily or permanently altered. The third series of experiments are evaluating single neuron activity patterns (within neural areas defined above) of infant rats in response to physiological challenges. The results of these studies are compared to adult-rat responses to determine when homeostatic regulation matures.